1. Field of the Invention
The present invention relates to a control apparatus for an electric automobile that includes an electric motor coupled to a drive wheel.
2. Description of the Related Art
Hybrid electric automobiles that use both an engine and an electric motor as power sources and electric automobiles that use only an electric motor as a power source have been under development. The electric motor installed in these electric automobiles is coupled to a drive wheel such that a rotation speed of the electric motor varies in conjunction with a vehicle speed. In other words, the rotation speed of the electric motor increases in a high vehicle speed region, and therefore an excessive induced voltage may be generated by the electric motor. In response to this problem, an electric automobile in which a clutch mechanism is provided between the drive wheel and the electric motor so that the electric motor is decoupled from the drive wheel at a high vehicle speed has been proposed (see Japanese Patent Application Laid-open No. 2007-331632 and Japanese Patent Application Laid-open No. 2008-239041, for example). Thus, over-speeding can be prevented from occurring in the electric motor, and as a result, generation of an excessive induced voltage can be prevented.
However, in the electric automobiles described in Japanese Patent Application Laid-open No. 2007-331632 and Japanese Patent Application Laid-open No. 2008-239041, the electric motor is stopped at a high vehicle speed, making power generation impossible. Hence, when the clutch mechanism is disengaged for a long time during high-speed cruising, discharge may be continuously performed, leading to depletion of battery power, and regeneration may be insufficient, leading to a reduction in energy efficiency of the electric automobile.